Ophthalmic lenses have traditionally been formed as a single integral body of glass or plastic. However, lenses are now also fabricated by laminating two lens wafers together with transparent adhesive. Regardless of how they are constructed, ophthalmic lenses often include an anti-reflection coating to improve transmittance of visible light.
Attempts have been made to provide anti-static, anti-reflection coatings (for a variety of products), and these attempts have largely centred on the theory of producing an electrically conductive (and thus substantially static resistant) anti-reflection coating. However, in practice it has proven to be virtually impossible to produce an anti-reflection coating for an ophthalmic lens product where the coating is highly transparent and truly is substantially static resistant. Indeed, to the best of the applicant's knowledge, there are no anti-reflection coated lens products on the market that actually exhibit acceptable, repeatable and durable antistatic properties.
In this respect, it should be noted that the applicant considers a product to exhibit acceptable anti-static properties when, after the product's surface has been rubbed with a suitable fabric (such as a piece of foam, a lint-free cotton cheesecloth, or a 100% polyester lens cleaning cloth), it exhibits virtually no ‘small particle attraction’; namely, substantially no small particles (such as talc powder, dust, tissue pieces, etc) are attracted onto the surface. Such an acceptable anti-static result may be generally correlated with a static voltage value of 0 kV±0.1 kV when the surface is rubbed for one minute with, for instance, a piece of foam. Therefore, a value other than 0 kV±0.1 kV will generally indicate that a product is ‘static’ and shows ‘small particle attraction’.
It is an aim of the present invention to provide an anti-static, anti-reflection coating that is suitable for use with ophthalmic lenses, which coating exhibits acceptable anti-static properties together with high transparency.